Extract LazyBackgroundTaskQueue from ExtensionSystem.

extensions/browser/lazy_background_task_queue_factory.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef EXTENSIONS_BROWSER_LAZY_BACKGROUND_TASK_QUEUE_FACTORY_H_
+#define EXTENSIONS_BROWSER_LAZY_BACKGROUND_TASK_QUEUE_FACTORY_H_
+
+#include "base/memory/singleton.h"
+#include "components/keyed_service/content/browser_context_keyed_service_factory.h"
+
+namespace extensions {
+
+class LazyBackgroundTaskQueue;
+
+class LazyBackgroundTaskQueueFactory
+    : public BrowserContextKeyedServiceFactory {
+ public:
+  static LazyBackgroundTaskQueue* GetForBrowserContext(
+      content::BrowserContext* context);
+  static LazyBackgroundTaskQueueFactory* GetInstance();
+
+ private:
+  friend struct DefaultSingletonTraits<LazyBackgroundTaskQueueFactory>;
+
+  LazyBackgroundTaskQueueFactory();
+  ~LazyBackgroundTaskQueueFactory() override;
+
+  // BrowserContextKeyedServiceFactory implementation
+  KeyedService* BuildServiceInstanceFor(
+      content::BrowserContext* context) const override;
+  content::BrowserContext* GetBrowserContextToUse(
+      content::BrowserContext* context) const override;
+
+  DISALLOW_COPY_AND_ASSIGN(LazyBackgroundTaskQueueFactory);
+};
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_BROWSER_LAZY_BACKGROUND_TASK_QUEUE_FACTORY_H_